Power converters are used to provide power from distributed generation sources for use on local loads or for delivery to a power grid. Such power converters are instrumental in applications such as for providing AC power from power sources like wind generators. With an increased societal focus on anthropogenic environmental degradation, particularly in relation to green house gas (GHG) and certain other emissions, there has been an increased trend towards distributed renewable power generation. For example, in recent years, there has been a steep increase in the number of wind generation farms that provide power to the power grid. Such distributed power generation sources may require power converters that are efficient, inexpensive, reliable, and have a minimal form factor.
A power converter for a renewable power source may include an inverter that is modulated by an inverter controller providing modulation signals. The inverter can have various topologies including two level or three level inverter. In a two level inverter, the modulation signal provided to each of the bridges of the inverter can have two voltage levels and the output power of each of the bridges of the inverter can have two levels, such as two voltage levels. Likewise, in a three level inverter, the modulation signal provided to each of the phases of the inverter can have three voltage levels and the output power of each of the bridges of the inverter can have three levels, such as three voltage levels. In general, three inverters with resulting three levels of modulation may be more efficient, resulting in reduced thermal losses in the inverter, than two level inverters with two levels of modulation. In other words, three level inverter modulation may result in reduced switching losses at low distortion per commutation period compared to a two level inverter modulation for similar modulation frequencies and power output.
The control signals, or modulation signals provided to the inverter phase legs are typically determined by an inverter controller using feedback from the inputs and the outputs of the inverter. The task of achieving a relatively high level of precision of inverter control for three level modulation can be difficult because the feedback signals provided to the inverter may not be consistent from one period of the inverter control signal to the next period of the inverter control signal.